This invention relates to the control of synchronous motors and more particularly to a state observer for estimating the angular orientation of the rotor of a synchronous motor such as a variable reluctance motor.
To obtain high performance from a synchronous motor such as a variable reluctance motor, its phases must be excited in synchronism with the position of its rotor. A shaft encoder or resolver typically provides the rotor position information necessary for this closed loop excitation. In some applications, the sensors are undesirable for reasons of cost, size, weight or reliability.
It is also known to infer rotor position by means of estimators for variable reluctance motors and permanent magnet motors driven by measurements of phase voltages and currents. These estimators primarily use zero crossing and peak detection to confirm coarse rotor motion rather than provide continuous position estimation. References [1-8] set forth in the accompanying Appendix report such position estimators. (Numbers in brackets refer to the references set forth in the Appendix.)
Observer theory is well developed for linear systems [9,10] and partially developed for non-linear systems [11-14]. However, the use of observers with electrical motors is rare despite the advantages they offer. Notable exceptions are concerned with the estimation of rotor flux in induction motors [15-17].
It is therefore an object of the present invention to provide an alternative to direct rotor position measurement for the control of synchronous motors.
Yet another object of the invention is an observer driven by measurements of phase voltages and currents for estimating rotor position continuously.
Still another object of the invention is a state observer able to determine rotor position to within one part in 50,000 of a mechanical cycle.
A still further object of the invention is such an observer which can be implemented with an ordinary motor controller forming a paint of synchronous motor systems.